Magnetic materials



atented App. 34 3%45 are mar oer-i manners maraaraas; Ethan a. Nesbitt, meant-n. N. a, assignor to Bell Telephone Laboratories,

incorporated,

New York, N. "2., a corporation oi New York No iiirawmg. hppiieation @otober 23, 1941 Serial No. 'dlt,2l9

i tlia.

by a stage of cold working during their preparation and prior to the final heat treatment. Such working is preferably accomplished by methods which produce elongation and prevent iateral spreading. Methods that have been iound beneficial include swaging, rolling with grooved rolls and wire drawing. It appears that the result of improved permanent magnet properties is manifested chiefly in the direction of, elongation Reduction of thickness by such rolling of a metal sheet as permits the material to'spread laterally is only partially effective.

The evidence is that materials of or produced according to the present invention generally are anisotropic and their improved properties are manifested chiefly in the direhtion in which the elongation takes place. i

In the Patent No.. 2,298,225 it'is pointed out that there are classes of materials which, if

maintained at a certain high temperature but below the melting point, assume a form known as the "gamma" phase, and if the material is thereafter cooled to around room temperature, it tends to assume the "alpha phase and thereafter it maintained at around 500 C. to 800 0., a finely dispersed small amount of the "gamma" phase forms in the fialpha" phase. This brief statement is to be read in the light of-the incopending application.

As pointed out in.Patent No. 2,298,225, dated October 6, 1942 a suitable procedure for prepermanent magnet material is to melt material and cool it to room temperature to produce formation of the "alpha phase and thereafter elevate the material to a higher temperature between 500 C. to 800 C. for a length or time such as is necessary to allow a small amount of the gamma phase to precipitate in a highly dispersed form in the "alpha phase.

formation. diagrams, and discussion of said This produces dispersion hardening in the ma terial and produces a very effective permanent magnet material. This method of forming permanentmagnet materials is different and seemingly involvesa difierent principle than that heretofore employed with respect to many others, such as alloys of iron, cobalt and molybdenum, in that in the present instance the material is converted into a low temperature falpha phase and thereafter has a small amount of the high temperature gamma phase precipitated therein in a fine and dispersed state. In the usual case of permanentmagnets hardened by precipitation the high temperature phase is preserved and a small amount of the low temperature phase is precipitated.

In some alloys of the type under discussion the "gamma" to alpha, transformation tends to occur at low temperatures at which the trans formation becomes sluggish and non-equilibrium conditions exist.

Whether this is the case or not, cold rolling these alloys in grooved rolls or working them mechanically by any equivalent method causes or expedites the formation at room temperature of the "alpha" phase and brings them into equilibrium. Some alloys of this type may not change completely to the alpha phase at room temperaturegupless given the above treatment.

Under the influence of the rolling treatment others change only partly to the "alpha" phase. Whether partial or complete this result is one beneficial aspect of the presentinvention. However, there is a second beneficial aspect which is due to crystal orientation. X-ray measurements confirm this and magnetic tests show the best permanent magnet properties in the. direction of elongation. Either or both of these aspects may be present in some degree.

After the alloys are brought into the ialpha" phase by the combination bi" coolingand cold worldng they are raised to a temperature which brings them to the temperature which causes the'precipitation in*flnely dispersed particles of some of the gamma" phase. This results in the production of magnetic material having efiective and desirable properties as permanent -magnets in the direction of elongation.- In

every casecare must )be used not to raise the material to too high a temperature in order not to lose the eiiect of cold working.

A frequently used criterion of the desirability of permanent magnet materials is the product of fccerciveforce and "residual induction." A more accurate figure of merit is that of marlmum energy product, which on the demagnetization portion of the hysteresis loop, is the prodnot of induction B and magnetizing force H at a point where this produce is-the greatest V See Wahl, "Applied Magnetism," pages 42 to 45, inclusive.

' The above criterion is independent of the matter of cost, ease or-difllculty of preparation rolling or drawing, brittleness, availability of raw materials and other factors which must receive consideration for many practical purposes and applications. Thus a permanent magnet composition which has an absolute maximum energy product less than some other which is less available or suitable from some one or more of the above aspects may be a valuable contribution to the art, if, for example, it may be made to possess a consistently greater maximum energy product." I

Among objects of the present invention are to aesaeea provide better permanent magnets at little or no perature generallvintheregion 500' C.to80o' C. and maintained fora long time in the extreme bottom of-therange,onetoseveralhoursinthe middle and much less if the temperature is at the Percent Percent Pcemt Parent iron nickel msngmsae cobalt The iron content may vary between 70 and I0 per cent, the nickel 15 and per cent, the manganese4-and20 percent, and the cobaltiand I) per cent. Carbon overabout 0.1 per cent is absent and the magnetic properties are not dependent thereon. Appreciable quantities of other comknown to haveuseful permanent magnet properstrips having useful maximum energy products"; I

and to provide useful magnets from materials which maybe worked with facility.

The subject-matter of the invention or discovery comprises a range or group of magnetic alloys which by appropriate combined heat treatment and cold rolling or elongating treatment will have one or the other or both of the abovenamed magnetic'products or the coercive force or the residual induction increased in the direction of elongation by from one hundred to several hundred per cent as compared to the material in the cast or unsuitably heat treated or unsuitably worked condition.

A feature of the invention or discovery is the lack of any necessity for quenching the material in order "to improve its properties; however, quenching may be practiced without detriment and one of the beneficial aspects of the discovery is that the cooling rate may varywidely as convenience or necessity demands.

The alloys may be prepared in the form of rods. bars, wire or tapes. A suitable treatment for any specimen is first to give it the desired, amount of cold working plus a low temperature bake. No other heat treatment is necessary. Satisfactory results have been obtained with reductions in area of 75 per cent, although this exact amount is by no means critical.

In greater detail, the material is cast, which gives it the necessary high temperature treatment; it may be given a further or. special heat treatment at around 800 C. to 1300 C. The cooled material, which may be cooled to room temperature slowly or rapidly and must be cooled substantially below about 600 C., is forcibly elongated by rolling with grooved rolls, swaging, drawing: through dies or by combinations of these methods or by any similar method or methods so as to reduce the cross section in one or several steps over a range from a small amount to 'a reduction to a small fraction of the original cross section. The material is then heated to a temis it in the range 500' mon impurities may be present. These compositions exhibit substantial permanent magnet properties and are notably improved in properties by a treatment of the kind described. They may be prepared from raw materials which are ordinarily cheap and readily available. They exhibit ma netic properties increased around 100 per cent or more with the treatment described as compared with identical compositions. cast. The increase in energy product due to cold rolling alone may be considerably over 100 per cent as compared to the same material heat treated but not cold rolled.

The apparatus illustrated in the above-noted patent may be used to perform the cold rolling process.

The niahed magnets are magnetized by the usual methods.

- What is claimed is:

1. A magnetic composition comprising 72 per cent iron, 18 per cent nickel, 5 per cent manganese, and 5 per cent cobalt.

2. A magnetic composition composed of between '70 and 80 per cent iron, 15 and 25 per cent nickel, 4and20percentmanganese,and4and20per cent cobalt.

3. A composition according to claim 2 which has been forcibly elongated while cold and thereafter heated above 500 C. but not above soo' C.

4. An article having properties adapted for permanentmagnetusecomposedofanalloy comprising as essential constituents '12 per cent iron, 18 per cent nickel, 5 per cent manganese, and 5 per cent cobalt, produced by causing the alloy to pass through or into the temperature range of ;fro m 800 C. to 1300 C., cooling it substantially below 600' C., forcibly elongating the material in the cold condition, and thereafter maintaining it in the range 5U0' C. to 500 C. without exceeding about 800' 0., whereby the material is caused to have increased ability to retain permanent v '20 per cent manganese, and 4 and 20 per cent cobalt. produced. by causing 'the alloy to pass through or into the temperature range of from 800 C. to 1300 C., cooling it substantially b0- low 800 .C., forcibly elongating the material in the cold condition, and thereafter maintaining C.tol00'C.withoutenceedper cent iron, 18 per cent nickel, 5 per cent manganese, and 5 per cent cobalt, passing it into or through the temperature range 800 C. to 1300" 'C., cooling the material to'the general region of room temperature, forcibly elongating the material while cold, and thereafter maintaining it at 500 C. to 800 C., cooling it, and magnetizing it along the general axis of the direction of elongation.

7. The method of producing a permanent magnet which comprises composing an alloy of between 70 and 80 per-cent iron, 15 and 25'per cent nickel, 4 and 20 per cent manganese, and 4 and 20 per cent cobalt, passing it into orthrough the temperature range 800 C. to 1300 0., cooling the material to the general region of room temperature, forcibly elongating the material while cold, and thereafter maintaining it at 500 C. to 800 0., cooling it, and magnetizing it along the general axis of the direction of elongation. 

